Known automatic or automated motor vehicle transmissions generally have a parking lock, with which an output shaft of the transmission can be mechanically fixed. In addition to a purely mechanical system for actuating such parking locks via a mechanical functional connection between a selector lever that is operated by the driver in the interior of the motor vehicle and the parking lock in the transmission, electromechanical and electrohydraulic systems for actuating such parking locks are also known—for example from DE 4127991 C2—wherein the parking lock in the transmission is connected via an electrical functional connection to a selector device operated by the driver in the interior of the motor vehicle, and systems in which the parking lock is electromechanically, or, as the case may be, electrohydraulically actuated by means of a parking lock function implemented in an electronic control device of the transmission as a function of other operating parameters of the motor vehicle.
In addition, various methods of automatically engaging such parking locks are known. For example, U.S. Pat. No. 3,937,105 proposes automatically engaging the parking lock of the transmission, independently of the gear step selected by the driver, if an ignition circuit of the motor vehicle is interrupted, and at the same time, the motor vehicle is still coasting at a lower speed than a defined low threshold value.
From U.S. Pat. No. 4,892,014, a method is known according to which the parking lock of the transmission is automatically electromotorically engaged, on the one hand, when an ignition circuit of the motor vehicle is interrupted, and at the same time the speed of the motor vehicle is lower than a predefined low threshold value, and on the other hand, also when the driver's door of the motor vehicle is open, and at the same time, there is no weight on the driver's seat of the motor vehicle, and at the same time the speed of the motor vehicle is lower than the above mentioned low threshold value. In both cases, it is provided that when the parking lock is automatically engaged, a parking lock of the motor vehicle is also automatically actuated. U.S. Pat. No. 4,892,014 also proposes that when the ignition circuit is closed, but the drive motor of the motor vehicle is not operating, the transmission automatically shifts electromotorically into its neutral position, without the need for a request of such an action by the driver.
Finally, from EP 0 814 287 61, a function for automatically engaging the parking lock of an automatic transmission is known, wherein the parking lock in an automatic transmission is automatically engaged by the transmission control device, if the speed of the motor vehicle is zero, and at the same time the ignition circuit is interrupted, and at the same time, as an additional condition, a predefined period of time has passed since the interruption of the ignition circuit, or a vehicle door is opened, however, not later—as the only condition—than when the ignition key is removed from the ignition lock. In order to achieve a better vehicle availability, as a special feature in all three cases, the actuation of the parking lock is prevented when, immediately before switching off the engine or within a predefined period of time after switching off the engine, the driver has selected the gear step ‘neutral’ with the selector lever.